Replaceable filter elements are well known which can be located in a casing or housing and separate contaminants from a fluid stream. One such element is shown in Koivula, U.S. Pat. No. 6,187,191, which shows and describes a filter assembly, particularly for lubricating oil and hydraulic applications, that has a cup-shaped casing enclosing a replaceable element, and which can be “spun on” to a threaded joint of a device assembly. The casing includes a central perforated support pipe attached to an extension of a deep-drawn recess at the closed end of the casing, and projecting toward the open end. The element has a cylindrical shape with appropriate filter media, and a first annular end cap at one (lower) end that is received over and seals to the central support pipe. A joint ring bears against the open casing end and has flow openings for the incoming fluid stream. The element has an annular end cap at the other (upper) end, with an end flange with an outer annular edge that is received between and provides a seal between the casing opening and the joint ring. A central collar is sealing received within this end cap, and has a threaded interior to enable the element to be spun onto a threaded spud of the device assembly.
Radial flow openings in the upper end cap allow fluid flow through the flange to the outer periphery of the element, where the fluid then passes downward between the element and the casing. The fluid then passes radially inward through the media and perforated support pipe, and then axially upward and out through the collar to the device assembly. When the element becomes spent, the casing can be easily unscrewed from the device assembly, the joint ring removed from the casing, and the filter element removed and replaced. The components are then reassembled and spun back on the device assembly.
The filter assembly of Koivula provides a simple filter that is tightly sealed to the device assembly, and provides an instant notification (a visible leak) if a casing is replaced without an element installed.
While the Koivula filter has many advantages over prior designs, the radial flow openings in the flange of the upper end cap direct fluid downward, primarily in the axial direction along the outer surface of the element. This tends to cause the contaminants to agglomerate in the upper region of the element, and cause pressure drop there across, while the lower portion of the element is relatively clog-free. This uneven distribution of fluid and contaminants can lead to decreased performance, and reduced element life.
It is therefore believed there is a demand for an improved replaceable filter element for such applications that has lower initial pressure drop and increased contaminant-holding capacity, without significant overhaul or modification of the filter system.